U.S. Pat. No. 5,715,909, Stepladder Including a Bracing Shelf, describes a stepladder with a pivoting bracing shelf. The bracing shelf acts as a conventional pivoting shelf and a bracing mechanism to prevent accidental closing of the stepladder when the shelf is in the bracing position.
U.S. Pat. No. 6,116,379, Ladder Stabilizing Cross Brace, describes two types of ladder stabilizing system. In one type of system, the ladder has a shelf or triangulated structure that is hinged to one side of the ladder and can be connected to the other side of the ladder. In the second type of system, there is a folding cross brace with a folding compound hinge that extends, when unfolded, diagonally across the ladder.